Gear pumps enjoy wide acceptance in many fluid pumping applications. To drive a gear pump, it suffices to impart rotary movement to one of the pumping wheels through the drive shaft and coupling connecting to a prime mover, such as an electric motor. The rotary motion will be transmitted to the idler shaft through the arrangement of meshing projections disposed on the pumping wheels and the engaging surface between the pumping wheels and both shafts. In many instances where such pumps are used, it may be desirable to orient the inlet and outlet ports on the pump casing to suit a wide variety of product handling configurations where the product supply reservoir may be positioned in a variety of locations along some vertical axis with respect to the actual position of the pump. Typical configurations would include placement of the reservoir above or below the pump as the situation dictates.
When pumping contamination-sensitive fluids such as food products or pharmaceutical fluids, it is also commonly required to disassemble, clean and reassemble the pump on a daily, if not more, basis. A pump that can be quickly dismantled, easily cleaned and rapidly brought back into service would present itself as being particularly advantageous. Functioning surfaces that are in contact and move relative to each other tend to produce unwanted particulates abraded from those surfaces. It is desirable to minimize the production of unwanted particulates, and as such, a pump whose functioning components are able to find the position of least communication with each other within the pump would be advantageous.
Where possible, it would also be advantageous to substantially transfer various abrasion producing forces to a member exterior to the pump casing. It is also desirable to have a gear pump with a limited number of ingress points to minimize possibilities for contamination of the sensitive fluids that are typically handled in food and pharmaceutical packaging environments.
A functioning gear pump must contain certain elemental features. These features can be present in a wide variety of configurations that may reflect the application, cost considerations and experience of the designer. In most gear pump designs, there is typically a need for one or more pumping wheels, a means for transferring rotational forces from a prime mover to at least one pumping wheel, a means for providing support and a guide for at least one shaft on which at least one pumping wheel is disposed, a means for maintaining a separation between the fluid being pumped and outside contaminants, a means for keeping the various members assembled and a means for maintaining a preferred alignment of the functioning members.
Conventional so-called gear pumps in existence typically handle the required internal functions in a wide variety of ways. However, they tend to include the need for threaded fasteners, integrally applied to hold the various pump components in a preferred relationship to each other. This method of construction where through bolts or threaded rods go through various machine members is often referred to as ‘tie-rod’ assembly, and is quite common in pneumatic and hydraulic cylinder assembly where one or more threaded rods are used to effect end cap retention on a cylinder.
An example of this kind of pump with ‘tie-rod’ construction would be the ‘Steripump’, which is sold by Nova Packaging Systems, 7 New Lancaster Road. Leominster, Mass. 01453. This pump features a plurality of stacked wafers that include end blocks, end caps and a member disposing a gear chamber. The assembly is held together with three threaded fasteners that go through the various wafers that make up the pump assembly. The issues associated with this mode of construction include a plurality of exposed circumferential gaps between the wafers that require the need for multiple o-ring face seals between adjacent wafers. The wafers themselves each require three openings for the passage of the threaded fasteners. With this type of construction there are associated assembly, disassembly and cleaning issues. If there is a deviation from the intended geometry of the pump components, tie-rod construction may inadvertently force pump members to possibly attain a location within the bolted-together stack of components which may not be the location of least communication between the members. As well, a further result of possible misalignment of the pumping chamber with respect to the pumping wheels would be friction that may tend to abrade one or more of the surfaces in contact to produce unwanted particles from those surfaces. Those particles would undesirably mix with the fluid being pumped.
One of the goals of the current invention is to minimize the production of particles abraded from the working surfaces of the pumping components.
Conventional gear pump bodies are typically mounted to the prime mover in a restricted single orientation that may limit the possible configurations of the inlet and outlet ports.
It is a further goal of this invention to allow the user to conveniently orient the pump housing to suit the configuration requirements of the fluid pumping situation at hand.
Once again, referencing the ‘Steripump’ from Nova Packaging Systems, that particular gear pump can be mounted in only the configuration that is arranged by the factory at the time of ordering the pump. One arrangement offered in their ‘Fillit’ machine offers a substantially bottom inlet port and another model, the ‘Power Fillit’ offers a substantially top inlet port. Modification of the factory-supplied arrangement by the user to suit a different supply reservoir arrangement would require extensive and impractical modifications to the host machine.
U.S. Pat. No. 5,755,566 Marsillo, et al. entitled ‘Self Driving Fluid Pump’, discloses an innovative pumping wheel configuration disposed in an arrangement of parts substantially held together by a ‘tie-rod’ arrangement of bolts. From the ‘Description of Preferred Embodiments’ in U.S. Pat. No. 5,755,566 we read: “The housing 12 includes a central portion 22 that is integrally formed with the inlet port 13 and with the outlet port 16. A top cover 24 and the bottom cover 26 are mounted on respective sides of the central section 22 by using suitable fasteners such as bolts 27. The top cover 24 differs from the bottom cover 26 by the provision of an aperture to accommodate the rotary shaft 18. This arrangement allows the pump 10 to be easily disassembled, simply by removing the bolts 27 in order to gain access to the internal mechanism for cleaning or maintenance.”
Swiftpack-King, Swiftpack House, 3 Arden Road, Arden Forest Industrial Estate, Alcester, Warwickshire, UK., offers their ‘King’ pump which features a similar threaded tie rod construction, this time with 2 threaded rods on either end of a member disposing a gear chamber through which the threaded rods do not pass. The member disposing the gear chamber is however rigidly maintained by tie rod assembly at some potentially variable location between the end blocks that are positioned on either side of the member disposing the gear chamber and pressed against the member disposing the gear chamber. This method of assembly may force the member disposing the gear chamber into a non-minimal cooperation with other members of the functioning gear pump assembly. The ‘King’ pump as well features pumping wheels that are pinned to their support shafts. In addition to previously mentioned issues with this construction, the pinned construction arrangement may present itself as a potential cleaning issue as there may be a requirement in some pumping applications to disassemble the pumping wheels for thorough cleaning during product change-overs and end of run conditions. A gear pump with fewer seals would also be advantageous and would constitute a significant improvement in terms of reducing potential leaks and possible ingress of unwanted materials. The prime mover side retaining end block of the ‘King’ pump assembly is threaded in two locations and the front end plate has clearance holes for passing the threaded tie rods. The two end caps each require o-ring face seals to prevent leakage and to reduce ingress of unwanted contaminants. This pump also features removable inlet and outlet port assemblies which require additional seals for containment of pumped liquid. Finally there is the drive shaft seal. In total, this pump requires five elastomeric seals for normal operation. As elastomeric seals are selected to be compatible with the chemical characteristics of the fluid products being pumped, it is necessary to have available an assortment of elastomeric seals molded from various compounds as each situation dictates.
Conventional gear pumps typically feature some alignment mechanism such as one or more alignment pins or reference marks, to ensure a preferred functioning alignment of the various required pump elements. This can be a source of error and damage when incorrectly assembling the pumps for preferred operation. The alignment pins require corresponding recesses. Both pins and recesses can be quite small. The pins can be easily lost or misplaced. The recesses are also an issue when it comes to cleaning or servicing the pump. It is a further goal of the current invention to provide a pump assembly where a single alignment element, an extended bushing, acting in communication with a receiving recess disposed in the pump body and coaxial with the drive shaft opening, is substantially the only alignment mechanism required to ensure that the pump has been assembled in the preferred manner.